1. Field of the Invention:
The present invention relates to a plasma separation filter, a plasma separation method using the filter and a plasma separation apparatus comprising the filter. More specifically, the present invention relates to a plasma separation filter capable of easily, speedily and safely collecting a small quantity of plasma necessary for blood tests or the like. The plasma contains subtially no blood cells and/or hemoglobin and retains substantially the same composition of protein and electrolytes as in the blood. The present invention also relates to a plasma separation method using the filter and a plasma separation apparatus comprising the filter.
2. Description of the Related Art:
Biochemical tests, which measure components in blood, are widely utilized for diagnosis and observation of progress for a variety of diseases, and occupy an important position as a clinical test. Analysis techniques for the biochemical tests have been significantly developed in recent years. For Example, the development of a variety of automatic analyzers has enabled a number of specimens to be accurately and speedily analyzed.
However, in some biochemical tests, the contamination of erythrocytes or the like interferes with the analysis of a targeted substance. Thus, plasma-or serum which is previously separated from blood is used. The plasma or serum for a test is obtained by collecting blood from a patient, followed by coagulation and centrifugation of the blood cell components. The operation of the coagulation and the centrifugation takes a long period of time, and thus not only prevents the period of time for the clinical test to be shortened, but also requires a large scaled centrifugal machine. Accordingly, except for large hospitals, the clinical test is generally only performed by external laboratories at the present. As a result of such outsourcing of the tests, several days are required to acquire the test results.
Thus, despite the automation of a number of processes for clinical tests, the separation of plasma is still mostly manually performed at the present. Therefore, the operation of separating plasma disadvantageously makes not only the clinical tests inefficient, but also puts a person involved at risk such as infection caused by contacting an infected blood.
A technique generally called dry chemistry is known as a means for solving the above-mentioned problem. According to this technique, when a trace amount of blood is dropped onto a small plate consisting of a serum separation layer formed of a micro fiber filter made of glass fibers or the like and a reaction layer located beneath the serum separation layer, the serum is separated in the serum separation layer. Then, the serum is reacted in the underlying reaction layer and colored, then measured by a spectrophotometer. In such dry chemistry, a liquid type coloring reagent is not used, nor is troublesome serum collection by centrifugation required. Although the dry chemistry is such a simple method, it has the following disadvantages: the number of measurable items is limited when compared with general biochemical analysis and immunological analysis using the liquid type reagent; a number of plates are required in order to test a plurality of items because one plate is used for one test item, thus impairing the advantage of shortening the operation time; and the dry chemistry is expensive. Accordingly, the dry chemistry is not widely used.
One example of means for speedily obtaining plasma is a separation method using membranes. Japanese Laid-Open (Kokai) Publication No. 53-72691 discloses a method for separating plasma from blood by using a fine tube-like filter device (pore diameter: 0.05 to 0.5 .mu.m) having one closed end as a filter medium. In this method, however, blood cells deposit on the surface of the membrane. Accordingly, a long period of time for filtering plasma is not only required, but also permeability of components such as protein contained in the plasma is poor. On the other hand, when filtering pressure is raised in order to raise a filtering rate, hemolysis (a phenomenon that erythrocyte membranes are ruptured and hemoglobin inside the erythrocyte is released) adversely occurs.
Furthermore, Japanese Laid-Open (Kokai) Publication No. 60-11166 proposes a method in which a filtering cartridge (pore diameter: 0.05 to 1 .mu.m) employing hollow fiber membranes is used so as to separate plasma from the blood. However, this method requires a priming (wetting the hollow fibers with saline) before separation. Thus, problems arises in that not only the preparing operation before the separation takes more time than the plasma separation itself, but also since the obtained plasma is diluted by the saline, accurate analysis data cannot be obtained.
In the aforementioned separation methods using membranes, a permeability of a relatively large molecular weight substance such as protein in blood is low because the separation is performed based on the molecular size. Thus, a composition of protein contained in plasma does not accurately reflect the original composition of protein in the blood. In addition, when the pore size of the membrane is too large, hemolysis adversely occurs due to erythrocytes clogged.
Other proposed techniques for separating serum or plasma for clinical tests using a fiber filter are as follows. Japanese Laid-Open (Kokai) Publication No. 61-38608 discloses a solid-liquid separation instrument formed of fibers using a volume filtering effect. In the solid-liquid separation instrument, plasma can be obtained by allowing blood to flow through the fibers while applying pressure. However, since pressure loss is large and thus resistance of a filter medium is large, several minutes are required to obtain plasma. In addition, since protein in the blood is adversely adsorbed in the fibers, a concentration of protein in the plasma obtained at an early stage is reduced. Thus, the solid-liquid separation instrument has not been practically used yet.
Japanese Laid-Open (Kokai) Publication Nos. 4-208856 and 5-196620 disclose a separation filter including glass fibers containing polyacrylate derivatives and polyethylene glycol, and lectin impregnated layer, a method for separating and collecting serum or plasma components using the filter and a device for separating serum or plasma using the separation filter. Although these methods and devices can collect serum or plasma for clinical tests without performing centrifugation, the serum or the plasma is obtained in amounts as small as about 100 .mu.l, and in addition, the period of time required for the separation is about 2 minutes. This is not so different from a period of time required when centrifugation is performed. Furthermore, since these techniques use glass fibers as a separating medium, electrolytes are eluted from glass fibers and blood components are adsorbed to the fibers. As a result, concentrations of electrolytes, phosphorus and lipid in obtained plasma or serum are significantly different from those in the original blood. For this reason, these techniques are not widely used.
As described above, no filter provides satisfactory performance to efficiently and safely separate plasma or serum components for use in clinical tests from a small amount of blood for a short period of time presents a sufficient performance at the present.